The present invention relates to a power connector with overvoltage protection for protecting an electrical operating station against excess voltages.
The protective measure called protective insulation, defined by VDE 0100/5.73.sctn.7 (Specification of the Association of German Electrical Engineers [VDE]), offers advantages in power connections, particularly for transportable operating stations.
These advantages include:
1. independence of the protective measures from the particular mains supply;
2. independence of the respective grounding conditions. Such transportable operating stations with protectively insulated power connections are known (VDE 0800, Part 2b/11.76 .sctn.20).
Protective insulation is a protective measure which is completely effective in itself without the participation of protective conductors and additional protective devices. With the use of protective insulation no malfunction is expected.
In the case of protective insulation a distinction is made between double and reinforced insulation, which can be seen from (VDE 0730, Part 1/3.72 .sctn.2b) 10 and 11, respectively. Double insulation is composed of the basic insulation and so-called supplementary insulation (VDE 0730 Part 1/3.72 .sctn.2b) 8 and 9, respectively. Basic (or functional) insulation denotes the insulation necessary for the functioning of the equipment and for basic protection against shock. Supplementary insulation denotes an independent insulation provided in addition to the basic insulation, in order to ensure protection against electric shock in the event of a failure of the basic insulation (1973 IEC Publication 435). In contradistinction to the supplementary insulation, the basic insulation is not immune from malfunction. Reinforced insulation is a single insulation which, however, is equivalent to the double insulation. However, its use is permitted only if it is obviously impossible to separately provide basic insulation and supplementary insulation (VDE 0730 Part 1/3.73 .sctn.220). Transportable operating stations, for example, directional radio stations, are often installed at locations where, or in the vicinity of which, lightning may strike, so that it is necessary to provide overvoltage protection. When a protection insulated power connection is provided, the overvoltage protection circuit must be as reliable as the protective insulation so that no malfunction, with the resulting excess touch voltage, can be experienced.
Measures for providing protection against overvoltages have become known in practice only in conjunction with protective measures provided by means of protective conductors and protective devices (VDE 0.100/5.73 .sctn..sctn.9-14) providing, for example, protective multiple earthing, protective earthing differential current earth-leakage protection, etc., but not in connection with protective insulation.
The VDE specification 0845 (DIN 57845) entitled "Protection of Communications Systems Against Overvoltages" describes an overvoltage protection circuit for the protectively insulated power connection of transportable operating stations in the telecommunications art according to VDE 0800 Part 2b/11.76 .sctn.20 (paragraph 3.11.6, FIG. 6).
Although this circuit meets the requirements of overvoltage protection, it does not meet the requirements of protective insulation when using commercially available overvoltage arresters. The latter have a limited insulation capability which may lead to quite dangerous situations since, for example, after a first response of the overvoltage arrester, its insulating resistance may drop considerably. A leakage current monitoring system for overvoltage arresters has therefore been proposed (VDE 0845a) for detecting a drop in the insulation resistance or for effecting the power connection by means of switches in the case of a malfunction, respectively. The grounding resistance of this protective system must lie below a given value, it must be checked and measured, respectively, and if it is used at the same location for long periods of time, it must also be monitored at given intervals, which requires a specially trained person.
Aside from the fact that sufficiently low grounding resistance can often not be realized at all, for example, when the system is installed on concrete, rock, sand, etc., it is very complicated and unsatisfactory for the user if safety in normal operation can be assured only by extensive monitoring and routine measurements. Such measures are also not within the spirit of the protective measure protective insulation, which is to provide completely autonomous and dependable protection to the user.